1. Field of the Invention
The invention relates to a plug-in coupling for connecting a fluid conduit to a pipe. The plug-in coupling comprises a pipe section having a first end section connectable to the fluid conduit and having a second end section into which the pipe can be inserted and locked so as to be sealed therein by at least one sealing ring inserted into the pipe section. The sealing ring is secured in its position between a securing ring attached to the pipe section and an inner shoulder of the pipe section.
2. Description of the Related Art
In a known plug-in coupling of this kind (European patent application 1 143 187 A2), the securing ring is provided radially inwardly with a peripheral flat rib which locks in a matching annular groove of the end section for receiving the pipe when combining the securing ring and the pipe section after insertion of the sealing ring. This locking connection cannot withstand high axial forces when pulling out the pipe from the pipe section.
It is also known to weld the securing ring to the pipe section. This type of connection of securing ring and pipe section is also not sufficiently durable because the pipe section cannot always be manufactured to be exactly round and the securing ring cannot be welded uniformly. In this configuration, the securing ring can also be pulled out of the pipe section together with the pipe inserted into the pipe section when releasing the plug-in coupling.
German patent application 196 09 925 A2 (FIG. 1) discloses a plug-in coupling that serves for connecting a fluid conduit to a pipe. The plug-in coupling has a pipe section whose first end section is connected with the fluid conduit and into whose second end section the pipe can be inserted, locked, and sealed therein by at least one sealing ring inserted into the pipe section. The sealing ring is secured in its position between a securing ring attached inside the pipe section and an inner shoulder of the pipe section. The pipe section has a slot extending in the circumferential direction of the pipe section; the slot receives the securing ring that contacts a support surface of the pipe section that is positioned opposite the slot. The securing ring is elastic and provided at its circumference with diametrically opposed radial hooks. It is inserted axially into the pipe section wherein the radial hooks, on the one hand, lock in an inner groove or recess and, on the other hand, in the circumferential slot. In order to remove the securing ring from the pipe section for exchanging the sealing ring, it must either be destroyed or one must attempted to compress it through the slot to such an extent that the radial hooks will become disengaged from the slot. However, since the radial hooks not only engage the slot but also the groove or recess opposite the slot, removal of the securing ring is obviously possible only after it has been destroyed; of course, this is costly with regard to material costs. If the radial hooks were to engage only the slot, no sufficient security in regard to the position of the securing ring and of the sealing ring relative to a frictional entrainment of the sealing ring by means of the pipe when releasing the plug-in coupling would be ensured. Moreover, the removal of the securing ring requires a simultaneous radial compression, and this is extremely difficult.